Next time you’re in a theater in Boston - or down on the Cape, or out in the Berkshires, or on Broadway, or pretty much anywhere, really - take a look around at the audience. Chances are you’ll notice something missing: young people.

What you’re likely to see instead is wave upon wave of gray hair. Most of the seats will be occupied by baby boomers and those of the generation born around the time of World War II. Thirtysomethings will be scarce; twentysomethings will be even scarcer. And teenagers? Don’t ask.

That question ought to be on the front burner this week as about 1,000 regional-theater professionals gather in Boston for the national conference of Theatre Communications Group, whose membership includes more than 500 theaters across the country. It’s been a persistent problem for years, and the American theater needs to find a concrete solution pronto, because its customers aren’t — you should pardon the expression — getting any younger.

In fact, there is reason to think the situation could soon get worse. As the cost of admission climbs ever higher, the advent of supply-and-demand-based “dynamic pricing’’ ensures that tickets to hot shows are as expensive as the market will bear. On Broadway, there’s the additional scourge of “premium seats,’’ which for “Death of a Salesman’’ and “The Book of Mormon’’ have commanded nearly $500 apiece. Theater, an inherently expensive art form to make at the professional level, is in danger of becoming a boutique business.

And the millennials, so financially strapped that they’ve been dubbed “Generation Debt,’’ might well feel that they’re in no position to be regular patrons. Saddled with college loans and credit-card payments, many bring home anemic paychecks if they’re lucky enough to have a job. Little wonder theater isn’t getting to be a habit with them.

Hard numbers on that are scarce, however. ArtsBoston has collected data on more than 1 million ticket-buying households, supplied by 50 cultural organizations in the Boston area. While the data have not yet been broken out according to individual genres — theater, music, dance, visual arts — they do provide a general demographic snapshot of local cultural consumers.

“We know that baby boomers are overrepresented,’’ said Catherine Peterson, executive director of ArtsBoston, the largest arts service organization in Greater Boston, which assists cultural organizations with marketing and audience development. “That’s no surprise. The under-30s are underrepresented.’’

The theater community, she added, has signaled a clear commitment to change that.

They need to, because the age divide is plain to anyone who spends any time at all in playhouses. Like most theater critics, I see several plays a week, not just on opening nights, and not only in large theaters. Almost invariably, the overwhelming majority of the audiences are middle-aged or older. What has always puzzled me about this is that the Boston area is home to an estimated 250,000 college students from September to June.

In other words, there is a huge population of 18-to-22-year-olds at more than 65 colleges and universities, quite a few of whom are eager, even desperate, for something to do off-campus on the weekends. Many who go to college here settle down in the area after graduation; they are the logical foundation of Boston theater’s future.

So, theoretically, Boston should be the perfect laboratory for experiments in how to attract young adults to the theater, right? And there is some experimentation going on, notably at Oberon, the American Repertory Theater’s second stage, where the programming tends toward the hip and late-night. Even Broadway musicals can give a company a breakout hit with an audience it doesn’t usually attract. That’s happening now with the Lyric Stage Company’s “Avenue Q,’’ which, thanks to a virtual stampede of young patrons, has shattered Lyric box-office records that go back four decades.

But such youthful audiences are exceptions to the rule.

On Broadway, theatergoers aged 18 to 34 made up less than a quarter of the audience in the 2010-11 season, according to the Broadway League, the trade association for theater owners and producers. The average age of a theatergoer was 44, but even that understates the case: At plays, the average age for audiences was 53, while the average spectator at musicals was 43.

Of course, many people experience Broadway productions not in New York but when the shows go on the road. And there, the evidence is even grimmer. According to the Broadway League, which surveys national touring productions in alternate years, the average age of those theatergoers in the 2009-10 season was 54.

As for regional theaters, figures on audience ages are hard to find. Theatre Communications Group, a service organization that surveys its member theaters on many aspects of the field and annually releases reports on attendance, performances, and finances, does not collect such data. In an interview, TCG executive director Teresa Eyring said theaters have not pressed for a nationwide survey of audience demographics. Local numbers, she said, are more useful to them.

“For us to get demographic data, our theaters would have to be surveying their audiences on a regular basis, and to do it correctly is quite pricey,’’ said Eyring. “It’s a very expensive proposition.’’

Perhaps, but most industries would consider it worth spending money on market research that tells them who their customers are - and aren’t. The need to reach young audiences has long been the subject of much private fretting by artistic directors and other theater professionals. It’s a challenge that, if met, might help address the lack of diversity that also afflicts many theaters.

“Theaters do need to be proactive in terms of engaging younger audiences, in making themselves inviting, whether that’s through the work or through education programs,’’ said Eyring. “It’s a way of ensuring that people have had exposure to it, to really get a taste of how exciting theater can be.’’

But she added a caveat. “I also think that theaters should love their audiences, whoever their audiences are,’’ she said. “There’s something wrong with the idea that there’s something wrong with audiences that are older. Theater should be for everyone.’’

Amen to that. But too often “everyone’’ does not include people under 30. For nearly a decade, I’ve taught at a local university while periodically guest-lecturing at a half-dozen others. It adds up to a lot of time on college campuses and many conversations, in classroom discussions or one-on-one, with hundreds of students. I listen as they talk excitedly about an upcoming rock concert or movie or football game. But theater? No. Except for a vanishingly small handful of theater majors or performers, students do not mention theater as part of their weekend plans or even as a presence in their lives. (One exception: An animated discussion broke out in one of my classes about the scarcity and expense of tickets to, what else, “The Book of Mormon.’’)

Let’s stipulate that some of the onus is on college students themselves, who fail to avail themselves of sometimes massively steep discounts. Too many are content to blow 20 bucks on a few beers when $15 and a ride on the T would buy them some theater magic. Intellectual curiosity and a spirit of cultural adventure are, or should be, cornerstones of higher education.

These students literally do not know what they are missing; there is general agreement that theater in Boston, in terms of what’s happening onstage, is in a dynamic phase at the moment. But theater is an art form that depends for its vitality on the audience - and there can be an extra jolt of electricity in the atmosphere when that audience consists primarily of young people, as with the raucous performances of Green Day’s “American Idiot’’ at the Boston Opera House in January.

Granted, theatergoing is a pastime that people often age into. And to an extent, the aging of the theater audience reflects the aging of the general population, as well as the wealth divide between old and young.

Still, though they’ve made some efforts, theaters are obviously not doing enough to reach young audiences.

Since the great majority of the hoped-for audience - twentysomethings and thirtysomethings - is usually not eligible for student discounts, why not follow the lead of companies that aim beyond the student population? In Boston, the Huntington Theatre Company offers $25 tickets to any show for those 35 and younger. Prominent theaters elsewhere make the tickets even more affordable for the same age range: $20 at both Manhattan’s Roundabout Theatre Company and the Chicago Shakespeare Theater, for example.

Because drama fans are made through early arts education, another part of the answer clearly lies in building a stronger presence in the schools. Social media and other marketing tools should also be used more imaginatively (but no “tweet seats,’’ please) to communicate the unique excitement of live performance. Theaters could dive deeper into the talent pool of new playwrights and performers, which could lead to more work that young audiences would consider must-see material - and along the way lift the spirits, and possibly swell the ranks, of provocative dramatists, some of whom complain that older audiences are not adventurous enough.

It won’t be easy, but the American theater has to find the missing piece of this puzzle. The alternative is long-term decline.